Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$120.47	11.538%	$134.3698	$134.37	$134.35	$134.40
Purchase #2	$100.32	5.461%	$105.7985	$105.80	$105.80	$105.80
Purchase #3	$97.88	11.232%	$108.8739	$108.87	$108.85	$108.90
Purchase #4	$165.59	11.683%	$184.9359	$184.94	$184.95	$184.90
Purchase #5	$155.93	11.336%	$173.6062	$173.61	$173.60	$173.60
Purchase #6	$87.89	9.659%	$96.3793	$96.38	$96.40	$96.40
Purchase #7	$16.56	11.389%	$18.446	$18.45	$18.45	$18.40
7 purchase totals =	$744.64		$822.4096	$822.42	$822.40	$822.40